Cutter

ABSTRACT

A blade assembly for a lawn mower has a generally planar body (1) rotationally balanced about a vertical central shaft (24), with four projecting blades (6) extending radially from the periphery of the planar body. The planar body (1) is shaped with vanes (3) to form a fan-like impeller. The impeller is arranged to create a strong rotational flow, which carries air and cut material around the blade assembly in use. The projecting blades (6) create an updraft in a peripheral region of the blade assembly, while the vanes (3) of the planar body (1) are shaped to create a regulated, relatively light downdraft towards the central shaft (24). If the mower is provided with an outlet (25) for a catcher, the strong rotational flow overwhelms any influence of the relatively light downdraft, and the air with the clippings is carried centrifugally through the outlet (25). If the outlet (25) is closed or the mower has no catching facility, the air and clippings continue to flow around the blade assembly in a turbulent, shallow spiral inwards and downwards, to be discharged as a mulch into the lawn under the mower.

FIELD OF THE INVENTION

The invention relates to the general field of lawnmovers and othercutting apparatus of the rotary type, with particular application todual discharge lawn mowers, wherein the grass, leaves and the like caneither be cut and discharged via a discharge chute in the blade housing,(referred to herein as catching or scattering"), or alternatively cutinto smaller particles and dispersed back onto and into the lawn,(referred to herein as "mulching").

BACKGROUND OF THE INVENTION

Lawnmowers have generally hitherto been designed either to catch lawnclippings in a catcher for disposal, or to recut or mulch clippings anddischarge them back into the lawn.

Prior art lawnmower blades, whether disc and flail blades or bar typeblades, designed for ejection of the clippings via a discharge chute inthe blade housing do not mulch and disperse the clippings satisfactorilyback into the cut lawn even when mounted to a lawnmower housing designedfor this purpose.

Lawnmower blades designed for mulching and discharge of clippings backinto the lawn often fail to operate satisfactorily in wet grass, andalso do not satisfactorily perform catching or scattering of clippings,especially if the discharge chute is disposed rearwardly in the bladehousing. Various forms of blades have been designed for the purpose ofcutting and mulching the grass and dispersing of the clippings back intothe lawn, as described in U.S. Pat. Nos. 2,809,488, 3,003,298,3,382,653, 3,531,923, 4,134,249, 4,292,791) and 4,617,788.

These mulching blades typically produce uplift and/or downdraft, whichin conjunction with a suitably shaped blade housing causes a cycling ofair and clippings substantially inwards and downwards as the means fordispersing the clippings into the lawn, and do not perform saiddispersal satisfactorily when fitted to a lawnmower with restrictions orvariations in the height of the blade housing, such as a raiseddischarge runway.

The prior art includes attempts to achieve dual operations, eitherdischarging clippings into a catcher or alternatively dispersing thesame back into the lawn, such as in U.S. Pat. Nos. 3,085,386, 3,132,457and 3,192,692, which show a mulching assembly with allowance for adischarge opening in the blade housing.

The housing does not include a raised discharge runway to facilitatedischarge of the clippings into a catcher, as such a runway would tendto disrupt the aforementioned cyclical airflow and adversely affect thedispersal of the clippings into the lawn when mulching. The dischargeopening is positioned on the side, rather than the rear of the bladehousing to allow removal of the clippings from within the blade housingas soon as possible.

The catching performance is relatively poor because this type of bladedoes not produce significant circumferential circulation within theblade housing to effectively eject the clippings out of the bladehousing and into a catcher. The inwards and downwards circulationgenerated by the prior art mulching blades causes a substantialproportion of the grass clippings to be recut before being dischargedfrom the blade housing when catching. This mices moisture and juicesfrom the clippings, which can cause clogging and make emptying thecatcher difficult, especially if the grass being cut is wet or lush. Anappreciable portion of the clippings also tend to be dispersed into thelawn in the process. The fine mulch does not lend itself to beingdischarged with sufficient energy to compact well into the catcher.

Furthermore, said prior an bar type blades exhibit a noted tendencytowards bending or deforming the engine or blade shaft to which they areattached at times when certain obstructions are encountered, due to theend of the blade being forced downwards as it moves forwards under theobstruction. This is due in pan to the particular configuration of theextreme outer cutting tip.

A further problem encountered with the prior blade mentioned above isthe tendency to enwrap certain types of leaves, especially long leavessuch as flax, as well as pieces of rope or cord encountered on the lawnaround the crankshaft, due to the upwards and inwards flow of air, whichtends to carry such material towards the crankshaft.

Mulching blades by and large suffer from a relatively high level ofabrasion due to the presence of the cut material, including grit beingheld in circulation within the blade housing before being dispersed ontothe lawn. This extra wear loading affects the outer end, especially thecutting edge as well as the lifting from the trailing edge,necessitating replacement of the entire blade assembly because of wearmainly at these points. The sharp cutting edge of the prior an bladediscussed tends to become blunt and deformed when obstructions to theblades travel are met.

The prior an includes a number of embodiments which utilize a fan orperforate disc for producing airflow and/or downdraft, such as thosedescribed in U.S. Pat. Nos. 2,737,772, 2,796,714, 2,888,796, 3,110,996,3,170,276, 3,220,170, 3,905,181 and 4,161,096 in an attempt to addresssome of the above-mentioned drawbacks. These blade systems are designedto work by and large in conjunction with a particular blade housingconfiguration, and do not satisfactorily mulch nor necessarily effectsatisfactory catching of discharged clippings when affixed to othercommonly used lawnmower housings.

A noted drawback with conventional disc and flail blades is thepossibility for the flail blade to rotate backwards and strike the bodyof the disc at times when an obstruction is encountered. This not onlytends to damage or deform the flail blade and the disc itself, but mayat times result in jamming of the flail blade below the disc body,requiring freeing manually at the expense of safety and convenience.

None of the above systems address the range of disadvantages noted aboveto a satisfactory degree, nor provide a cutting system which can betransported to a variety of blade housing configurations and maintainsatisfactory performance whether catching, scattering or mulching thegrass clippings and the like.

OBJECT

It is an object of the present invention to go at least partway towardsproviding a novel improved rotary blade assembly, or at least to providethe public with a useful choice.

DEFINITION OF TERMS

"Lawnmower" refers herein to a device used generally for mowing ortrimming grass and other types of vegetation, conventionally powered bya small internal combustion engine or electric engine.

"Catching" refers herein to the process of ejecting cut clippings andthe like from the blade housing via a discharge chute and into anattached container which collects the clippings.

"Mulching" refers herein to the process of recurring the clippings andthe like into smaller pieces and also dispersing these pieces down ontoand into the lawn.

The "solidity ratio" refers herein to the area of an article in planview given as a fraction of the total plan area swept by that article inrotation. For instance, of the total area which an article covers in onerevolution about its axis of rotation is considered as 1.0, an articlewhich occludes half of this plan area has a solidity ratio of 0.5, whilea solid circular disc, which occludes the whole area swept in rotation,would have a solidity ratio of 1.0.

The "face area" refers herein to the radially and axially extendingsurface area of a rotatable article, relative to its axis of rotation,including any inclined or curved surfaces which have a radial and anaxial component.

"Rotational circulation" refers herein to the movement of air along withentrained lawn clippings and the like around the central axis of theassembly.

"Circumferential circulation" refers herein to rotational circulationaround the peripheral portion of the blade assembly.

"Angle of incidence" refers herein to the angle made from thehorizontal, commonly known as the angle of attack, across the chord ofan object.

SUMMARY OF THE INVENTION

A blade assembly according to the present invention includes:

means for mounting on a central shaft;

a generally planar body substantially evenly disposed about said meansfor mounting on a shaft, comprised of an inner region and a peripheralregion:

means for cutting in said peripheral region;

means for creating updraft in said peripheral region;

means for creating downdraft in the inner region;

and means to create a rotational airflow, comprised of a radially andaxially extending face area of said body, by which air can be moved assaid body rotates on said shaft;

wherein the said face area of said inner region is greater than the facearea of said peripheral region.

Preferably the inner region has a plan solidity ratio greater than 0.5.

Without limiting the generality of the forgoing, the preferred form ofthe present invention provides means for producing primary airflowsincluding updraft and rotational circulation; and secondary airflowswhich include swirling and eddying of air, tip vortices, and downdraft,wherein the secondary airflows are regulated so as to be insignificantrelative to the primary airflows when the assembly is used in an openhousing, but to take effect when the assembly is used in an enclosedhousing.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present invention will be better understood withreference to the following detailed description of a preferredembodiment, given by way of example, with reference to the accompanyingdrawings, in which:

FIG. 1 shows a perspective view of a first preferred blade assemblyaccording to the present invention attached to a rotary lawnmower, asseen from below.

FIG. 2 shows a perspective view of the first preferred blade assembly,as seen from above.

FIG. 3 shows a schematic perspective view of the first preferred bladeassembly.

FIG. 4 shows a plan view of the blade assembly.

FIG. 5 shows a side view of the blade assembly, as seen in the directionof arrow A in FIG. 4.

FIG. 6 shows a cross-sectional view of the assembly as seen along lineB--B in FIG. 4.

FIG. 7 is a diagrammatic representation of the airflows produced by thepreferred blade assembly.

FIG. 8 is a diagrammatic representation of the path of cut clippings ina radial plane wig the blade housing.

FIG. 9 shows a plan view of the preferred flail blade.

FIG. 9a shows an end view of the flail blade of FIG. 9.

FIG. 9b shows a front view of the flail blade of FIG. 9.

FIG. 10 shows a perspective view of a second embodiment of theinvention.

FIG. 11 shows a perspective view of a third embodiment of the invention.

FIG. 12 shows a perspective view of a fourth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In its preferred form as illustrated in FIGS. 1 to 9, the inventionprovides a blade assembly for lawn mowers which may be used in differentways to achieve different results. In particular, the preferredembodiment may be used for:

1. Mulching of grass clippings and the like if discharge chute issuitably enclosed.

2. Dispersing clippings by scavenging such from inside the blade housingand dispersing such onto and into the lawn of the discharge chute issuitably enclosed.

3. Catching of grass clippings, leaves and the like via a dischargechute in the blade housing if said discharge chute is open.

4. Scattering of said clippings via a discharge chute in the bladehousing of said discharge chute is open.

The illustrated catching and mulching blade assembly is, according tothe present invention, adapted to be installed in a conventional rotarylawnmower which, as shown in FIG. 1, conventionally includes a bladehousing 21, a discharge chute 25 for ejection of lawn clippings, a motor22, and wheels 23. The motor 22 is provided with a depending shaftprojection 24 which extends downwardly into the space within the bladehousing 21, to the lower end of which the catching and mulching bladeassembly is attached with the use of an annular flange or similarmounting device as per conventional disc assembly detail.

Alternatively, the mulching and catching blade assembly is attached to ablade or drive shaft which is affixed to the blade housing 21 and drivenremotely from the engine 22 by means of belts, chains, hydraulics orsome other means (not shown).

The preferred blade assembly as shown in FIG. 2 comprises a central discbody 1 with a central mounting point 2 arranged for mounting on theshaft 24, and a number of vanes 3 radiating from said body 1, withapertures 4 between said vanes 3, and a number of primary blades orflail blades 6 extending from the periphery of said vanes 3. The centralbody 1 and vanes 3 comprise an inner region of the assembly, while theextending blades 6 comprise a peripheral region of the assembly, asreferred to hereafter.

The disc body 1 is preferably made of a suitable metal, although othersuitable materials could be used. The center of the disc body 1 ispreferably raised somewhat above the cutting level of the blades 6 tofacilitate various mounting attachments at the mounting point 2 and toprovide clearance.

The vanes 3 are raised to a peak 13 partway along the leading edge 9,and slope downwards towards the root and the tip of the vane 3, andtowards the trailing edge 8, to form a scoop or pocket 10, as shownschematically in FIG. 3. The inner region of the blade assemblyaccordingly acts as an impeller or fan. An area near the trig edge 8towards the vane tip is made substantially flat to form a blade mountingarea 5, and for reasons of rigidity and structural integrity it ispreferable that the vanes 3 are cambered to create a ridge or rib 11extending from root to tip, as represented in FIG. 3.

The leading edges 9 of the vanes 3 are preferably hardened and sharpenedso as to form secondary cutting blades 14, as shown in FIG. 2. Thissharpened edge 14 may be ground, pressed, machined or formed by die eastfrom the material of the vane 3, or alternatively formed separately andthen affixed to the vane 3 by welding, rivetting or some other suitablemeans.

The tips of the vanes 3 are preferably made substantially square and ofat least similar or greater chord W than the root of the vane 3, inaddition to being cambered and downwardly inclined, in order to enhancetip vortice formation as described hereafter.

The vanes 3 are preferably formed from the material of the disc body 1,being pressed and raised up at their leading edge 9 by a suitable tooland die, although it will be appreciated that this assembly may bedie-east or otherwise constructed as separate fabrications andsubsequently joined by welding, rivetting or other suitable means.

The blades 6 are preferably made of a suitable metal such as springsteel strip, although other suitable materials may be used, and arepreferably relatively thin and fiat with a suitably hardened andsharpened cutting edge 15 facing the direction of travel. The blades arepreferably mounted horizontally, and twisted down at the outer end so asto bring the cutting edge 15 to a point below any other part of theassembly, providing a clearance between the cutting height G and theunderside of the inner region, as shown in FIG. 8.

The blades 6 are also twisted upwards at the rear, which effectivelycauses the entire outer end section of the flail blade 6 to act as anairlift element 7, causing uplift U and circumferential circulation Caround the periphery of the blade housing. The elements 7 are preferablyinclined at an angle as shown in FIG. 9a great enough to induce stallingof airflow over the face of the flail blade 6, so as to cause suction intheir wake which draws the cut material orbitally around the bladehousing 21.

Replacing a set of highly twisted flail blades 6 with a set of blades 6with less twist will allow the performance of the blade assembly to becustomized for particular requirements, such as dedicated catching ordedicated mulching, in order to optimize the performance as desired.

The combined radially and axially extending face area of the blades 6,comprised largely by the upturned portions 7, should preferably alwaysbe less than the combined face area of the vanes 3 in the inner,impeller region. An important feature of the airflow generated by ablade assembly of the present invention is the relatively strongrotational flow, generated both at the periphery of the assembly and inthe inner, impeller region defined by the vanes 3, as detailedhereafter. To maintain sufficient airflow in the inner region, theimpelling faces in the inner region must be proportionately larger thanthose in the outer region, which move at a higher velocity when theassembly rotates.

A combination of blades 6 with more twist and blades 6 with less twistmight also be employed to tune the overall efficiency.

The blades 6 are preferably pivotally attached to the underside of thevanes 3 at mounting points 5 by means of suitable bolts 16 rivets orother methods, as are conventional flail blades. It is preferable thatthe blade 6 has at least partial rotation, so that of an obstacle isencountered during operation the flail blade 6 is able to rotatebackwards, as depicted by dashed outline 6' in FIG. 4. Fixed,non-pivoting blade tips could alternatively be bolted, welded orotherwise affixed to the vanes 3.

The position of the blade 6 mounting points 5 near the trailing edge 8of the vane 3 as depicted in FIG. 3 has been found preferable for masonsof causing less disturbance to airflow around the vane 3 and thegeneration of the tip vortices V, as well as allowing freedom ofrotation of the flail blade 6 as mentioned above.

The blade assembly herein described is preferably of a similar diameterto a conventional disc assembly, so that the length of the flail blade 6is in similar proportion to the overall diameter of the blade sweep asis conventional for a disc and flail blade assembly. The clearancebetween the flail blade 6 tips and the blade housing 21 is to be no lessthan the minimum permitted by the appropriate safety standards, andpreferably only large enough to avoid jamming of grass and the likebetween the blades 6 and the inside of the blade housing wall 28.

To give a typical set of dimensions:

With reference to FIG. 4, in a mower having a blade assembly which is500 millimeters total diameter overall, the diameter Z of the innerregion or impeller, comprised of the body 1 and vanes 3, will beapproximately 340 mm, the length L of the vanes 3 will be approximately100 mm, and the width of the vanes 3 will taper from approximately 115mm W at the tip of the vane to approximately 105 mm W' at the root ofthe vane 3. The separation X between the tips of the vanes 3 will beapproximately 140 min. This results in an inner region having a solidityratio of approximately 0.65.

With reference to FIGS. 5 and 6, the preferred height H of the leadingedge above the trailing edge of the vane will range from 8 mm at theroot and tip, to 16 mm at the highest point of the front edge 9. Theinner region impeller will preferably have a radially and axiallyextending face area of approximately 4000 mm², comprised ofapproximately 1000 mm² face area on each of the four vanes 3--the innerdisc body 1 has no radially extending faces, being circular. The facearea of the peripheral region, comprised largely of the upturned airliftelements 7 on the four blades 6, will be approximately 2800 mm²,comprised of approximately 700 mm² on each blade 6.

OPERATION OF THE PREFERRED EMBODIMENT

The preferred blade assembly of the present invention can operate ineither a mulching or a catching mode, depending on the nature of thehousing in which it is mounted. Preferably, the mower can be switchedfrom one mode to the other simply by opening or closing an outlet in thehousing, with no modification or adjustment to the blade assembly.

The primary airflows including the uplift U, the circumferential C andthe inner rotational R circulation are predominant over the secondaryairflows regardless of the environment of the blade assembly. Theprimary airflows are much more powerful than the secondary airflows, andtherefore have the greatest influence on the movement of the cutmaterial, namely to circulate it substantially around the periphery ofthe blade housing 21 in a shallow trajectory.

The influence of the secondary airflows is inconsequential if an outlet25 in the housing is open, because the primary airflows act to carry thecut material out through the outlet before the secondary airflows haveany significant effect. However, if the blade housing outlet 25 isoccluded so as to create a substantially closed environment, the primaryairflows result primarily in circulation of the material within thehousing, while the secondary airflows cause an alteration to thetrajectory of the cut material, and carry it inwards and downwardsthrough the vanes 3. Accordingly, the assembly can treat the cutmaterial in two different ways, depending on whether the outlet 25 inthe housing is open or closed.

CATCHING

For a catching operation, the housing is provided with an open outlet25, leading either into a catcher, or simply to the exterior. Clippingsare lifted and carried forwards on the airflow produced by the upturnedairlift elements 7 as the blades 6 cut the lawn, and are propelledstrongly around the housing in a continuous circumferential flow. Fromthis flowpath, the clippings are thrown outwardly through the outlet 25by the centrifugal, outward force of the rotational flow, for catchingor dispersal.

As noted above, the preferred assembly has a greater face area in theinner region (A2 in FIG. 6) than in the peripheral region (A1 in FIG.5), and has a solidity ratio in the inner region of greater than 0.5.Strong rotational circulation is augmented by the provision of a largeface area on the vanes 3 in the inner, downdraft producing zone, whichadds to the rotational flow produced by the elements 7 without similarlyadding to the updraft.

The downdraft produced by the vanes 3 is regulated by the high solidityratio of the inner region, described in more detail hereafter.Accordingly, inward flow F across the top of the assembly, resultingfrom peripheral updraft and central downdraft, is also controlled.Through the combination of a proportionately greater face area in theinner region than the peripheral region and a high solidity ratio, thevanes 3 are able to augment the rotational flow, without similarlyaugmenting the upward, inward and downward flow.

Inward flow is an impediment to good catching performance, so byrestricting this flow and augmenting rotational flow, the blade assemblyis able to enhance catching performance.

A tendency commonly noted with the prior art mulching systems when usedfor catching is to chop a large proportion of the clippings into smallparticles before discharging them from the blade housing (which releasesjuices and tends to cause clogging) due to the significant upwards andinwards airflows produced, The preferred embodiment of the presentinvention avoids this problem when catching, as the rotationalcirculation (R and C as shown in FIG. 7) is powerful enough to carry theclippings out the open discharge chute 25 before the inward airflow Fhas the opportunity to transport the clippings G1 to the inner cuttingblades 14.

Sufficient circumferential circulation C is generated in accordance withthe present invention to pre-empt the said secondary cutting, at leastup to the point where the clippings are able to be discharged (even ifthe discharge chute 25 is disposed rearwardly on the blade housing 21).

In accordance with the above statements, the clippings G1 dischargedfrom the discharge chute 25 during catching operations are thereforesubstantially bigger than the clippings G2 & G3 which are recirculatedand eventually dispersed back into the lawn when mulching.

The strong rotational airflow also helps to maintain a more effectivedischarge into the catcher in unfavourable conditions, such as whenmowing wet or lush grass, and helps to keep the inside of the bladehousing 21 clean, with less tendency for clippings to accumulate insidethe blade housing 21. This feature improves both the convenience as wellas safety of the lawnmower, as the user has less need to access theinterior of the blade housing 21 for periodic cleaning and unclogging,which access necessarily exposes said user to a certain degree of risk.

MULCHING

For mulching operation, the housing is closed. Preferably the dischargeoutlet is closed with a flap or block 26 which substantially fills anyasymmetric recess at the outlet in the housing wall. This causes theairflows within the housing to be recirculated in a closed environmentto some degree which allows the secondary airflows to become effective.

When mulching, the clippings are swept by the blade assembly through adifferent, extended series of operations from the simple circumferentialflowpath followed in a catching operation. It is to be appreciated thatthe present invention therefore performs two discrete operations,selected essentially by whether the discharge chute is opened or closedand a catcher fitted.

The overall processes involved in the mulching operation are as follows:

1. Grass and the like initially cut at the outer periphery of the bladeis imparted with compound motion both upwards and forwards into thecircumferential airflow C by means of the primary blades 6 and liftingelements 7, as depicted in FIG. 7, and as in the catching operationdescribed above.

2. The entrained cut clippings G1 are carried around the periphery ofthe blade housing in the circumferential airflow C in FIG. 8.

3. With no outlet in the housing the entrained clippings G1 insuspension in the circumferential airflow C spiral inwards due in partto continued uplift at the periphery generated by the flail blades 6 anddownflow induced more centrally by the vanes 3.

4. Upon reaching the proximity of the tips of the vanes 3, in theboundary area between uplift and downdraft, the clippings G1 are carriedsubstantially inwards and downwards by the inward flow F and tipvortices V, which reduces clogging of cut material on the underside ofthe housing 27 above the boundary area.

5. Once in the proximity of the vanes 3, the clippings are drawn betweenthe vanes 3 and chopped into smaller pieces by the secondary cuttingedges 14 on the outer end of the rotationally forward edges 9 of thevanes 3.

6. The smaller particles G2 & G3 are then in part dispersed into thelawn beneath the blade assembly by a combination of their own forwardmomentum and the airflows produced by the impeller, ie: the strongrotational circulation R, the downdraft D, the tip vortices V and theswirl S induced below the impeller.

7. Clippings which are not dispersed into the lawn may be drawn into thetip vortices V and rotated back into the recutting blades 14 where theyare eventually cut into free particles G3 and dispersed into the lawn,or may be lifted by the primary blades 6 to be recycled through theprocess.

The overall solidity ratio of the inner region and the axial depth ofthe vanes acts to limit the downdraft, so that it remains relativelyweak regardless of the housing configuration, the updraft, or therotational flow. This provides a benefit to both the catching operationand the mulching operation. With regard to catching, the downdraft actsto draw air and clippings inwards contrary to the centrifugal, outwardflow by which clippings are thrown into a catcher, and accordingly maybe detrimental to catching efficiency.

With regard to mulching, a certain amount of downdraft is beneficial, inthat it can carry clippings or mulch down into and onto the lawnbeneath. Too strong downdraft is however found to be detrimental in thatit tends to flatten the lawn beneath, interfering with cutting andinhibiting distribution of mulch under and amongst the lawn vegetation,and may also blow the mulch out from under the housing, forming windowsto either side. Furthermore, clippings may be carried through theassembly and blown out before being adequately chopped and mulched.

The generation of downdraft is controlled and regulated in the preferredembodiment of the present invention by the inclination and chord of theimpeller vanes 3, which create a strong, turbulent circumferential flowin the inner region.

When the housing outlet 25 is open for a catching operation, thedowndraft is overwhelmed by the strong rotational flow and flow outthrough the outlet 25, and has no significant effect on the overall flowof clippings. When the housing is closed however, the rotational flowsimply circulates air and cut material in a continuous, endless cyclearound the housing. Accordingly, the weak downdraft D and consequentinflow F gradually draws the clippings inwards and downwards as theyflow around, and finally carries them down into the lawn on a turbulent,generally shallow trajectory. In the turbulent flow created by the vanes3 the clippings G1 first cut by the blades 6 are recur on the vanes 3into smaller particles G2, and into smaller particles again G3 as theyare recirculated through the inner region by the overall recyclingeffect produced. Suitably sharpened cutting edges 14 present at least onthe outer portion of the leading edges 9 of the vanes 3 facilitate thisrecutting process.

The clippings and the like are swept into the lawn below the vanes 3 bymeans of both downdraft D and rotational circulation R as depicted inFIG. 7, which stirs the clippings and the like into the lawn to somedegree with a turbulent, swirling action S as depicted in FIG. 7 and 8,below the cutting height G. By this means the blade assembly stirs thecut lawn, and avoids flattening it with downdraft which may bedetrimental to good dispersal of the mulch.

Catching operation blade housings typically exhibit less clearance(depicted by K in FIG. 8) between the ceiling 27 of the housing and theblade assembly at one radial cross-section, and more clearance atanother, than that typical for mulching mowers. This results indifferences in the restriction of inwards or downwards flow.

The present invention achieves satisfactory performance with lesssensitivity to such variations in the airflow, as the assembly itself isthe most dominant influence on airflows in the dispersal area.

By generating strong circumferential C and rotational R circulation (incomparison to the downdraft) in conjunction with maintaining anacceptable downwards airflow D the effectiveness of the said dispersalis rendered more independent of the said inward and downwardcirculation, and the cross sectional shape of the blade housing.

An assembly with vanes 3 which are of more or less equal length andchord proportions, (depicted by L and W in FIG. 4) set at a downwardangle from the leading 9 to trailing 8 edges of the vane 3 in the orderof approximately 1 in 8, and which has a solidity ratio of more than 0.5has proven acceptable.

Incorporating a substantially fiat horizontal plane 5 at the trailingedge 8 of the vane 3 of approx. 25% of the overall chord W of the vane 3has proven to be an effective means of enhancing the rotationalcirculation R and the swirl S (depicted in FIG. 7 and 8), particularlyin the area of dispersal under the impeller, as well as providing adouble or reverse ember in the vane 3 for rigidity and a suitably flatarea for mounting the pivoting blades 6.

It has been found that while impellers with a solidity ratio as high as1 (in the case of an impeller which has vertical apertures between thevanes) can produce satisfactory results, the best results have beenobtained using impellers with solidity ratios in the range of 0.6 to0.8. Because of the lesser tendency towards clogging and lesser weight,an impeller with a solidity ratio near 0.7 is considered ideal.

A restrictive blade housing such as that depicted in FIG. 9 causesaccumulation of mulched particles and clippings on the underside of theceiling of the blade housing 27, notably in the boundary area betweenuplift and downdraft, referred to as clogging. This problem of cloggingabove the boundary area is somewhat remedied by the increasedcircumferential C and rotational R circulation within the blade housing21 generated by this new blade, as well as by the generation of powerfulrotational currents of air in this boundary area known as tip vortices,depicted by V in FIGS. 7 and 8.

Disposing the vanes 3 at a moderate downward angle from rotationallyleading 9 to trailing edges 8 (below the stall angle), createsdifferential air pressure above and below the vanes 3. Cambering thesaid impeller vanes 3 in a similar manner to an aerofoil such as anaeroplane wing, ie: upwards along the length L from the root to the tipof the vane 3, in the order of several percent of the chord W, furtherenhances this pressure difference, as well as improving the rigidity andresistance to flexing of the vane 3. This difference in pressureproduces vortices (V in FIG. 8) at the vane 3 tips (as opposed to randomswirling or turbulence).

The adoption of substantially square tips enhances the vorticegeneration, as does an increase in the chordwise span (depicted by W inFIG. 3) towards the tips of the vanes 3 in comparison to the chord atthe root of the vane 3.

The midpoint 13 of the vane 3 is raised to a greater angle of incidenceI than the root or tip portions, resulting in a gullwing shaped vane 3as depicted in FIG. 5. This allows twist-off towards the tip of the vane3 while maintaining the tip of the vane 3 at an incident angle (I' inFIG. 5) sufficient to induce useful vortice formation, withoutincreasing the overall angle of incidence of the vane 3 (which wouldcause overdrafting). Such a configuration further allows the formationof a lower pressure zone towards the center of the assembly whichreduces outflow O below the impeller to some degree, and directs airflowtowards the center of the assembly.

The tip vortices V result in significant localized toroidal airflowabout an axis along the path of rotation of the tips of the vanes 3,upwards and inwards over the outside edge of the tips of the vanes 3 andthen downwards and outwards again behind each vane 3, as depicteddiagrammatically in FIG. 8. This vortex rotation V is substantiallyinwards at the top of its cycle, complementing the overall inwards flowof the clippings towards the vanes 3, and therefore contributes towardsindependence of the airflow from the cross-sectional configuration ofthe blade housing.

The generated tip vortices improve the overall airflow disposition andentrainment of clippings in suspension and may contribute towards adecrease in the above-mentioned problems, namely clogging of cutmaterial in the boundary area above the vane 3 tips, as well asimproving the dispersal of the recut clippings. The rotation induced bythe said tip vortices V also aids the upward and inward airflow producedby the flail blades 6 to lift the clippings, depicted by G1 in FIG. 8,and helps transport them inwards for further circulation through thedispersal area. Thus, a significant proportion of clippings G2 & G3 canbe kept in suspension and recirculated within the blade housingsubstantially above and in the vicinity of the impeller, regardless ofvariations in the cross-sectional shape of the housing 21, as depictedin FIG. 8.

It is to be appreciated that a wide variety of changes and modificationsmight be made to the above example within the general scope and spiritof the invention. As shown in FIG. 10 a reinforcing ring 31 of suitablematerial may be affixed towards the outer end of the vanes 3, in orderto provide stiffness to the impeller assembly.

The application of ribs 11 as shown in FIG. 3, pressed into the vanes 3and extending radially towards the center of the disc body 1 somedistance has been found to provide a satisfactory degree of stiffness tothe vanes 3, obviating the application of reinforcing ring 31.

It has been found that while using impellers with two or three vanes 3achieves acceptable results in some instances, four vanes 3 with fourblades 6 attached, as depicted in FIG. 2, produces especiallysatisfactory results for both catching discharged clippings oralternatively dispersing mulched clippings back into the lawn on avariety of housing configurations. Four vanes 3 allows provision of foursecondary cutting blades 14, resulting in more effective recutting ofthe grass clippings G1 than by two or three. Likewise, four vanes 3 andconsequently four vane tips are more effective in producing the primaryand secondary airflows and dispersal mechanisms described above than twoor three.

The provision of four primary blades 6 for cutting and uplifting thegrass clippings G1 reduces the mount of cutting performed by each blade,thereby enhancing the fineness of the cut and the effectiveness of eachprimary blade 6 and lifting element 7. More even propulsion is alsoprovided by the use of a multiplicity of primary blades 6 (at least fourpreferably) with uplift producing elements 7.

Although some slight advantage may be perceived with the application ofa greater number of vanes 3 or flail blades 6 or both, for reasons ofpracticality, cost, weight and reliability four vanes 3 in conjunctionwith four flail blades 6 are considered optimum for producingsatisfactory results.

The vanes may be substantially flat or uniform along their radiallengths, as an alternative to the "gull-wing" form illustrated in FIGS.1 to 9, although this is considered less preferable at present.Inclining the mounting area 5 on the impeller vane 3 upwards towards therear edge 8 of the vane 3 (so as to angle the flail blade 6 upwardstowards the trailing edge according to rotation) improves theperformance of this system for catching of discharged clippings, andallows the flail blade 6 to pivot upwards and backwards if anobstruction is encountered. However, the induced downflow consequentlydecreases, with a corresponding drop in performance when mulching anddispersing the clippings back into the lawn.

The mounting point 5 of the flail blade 6 is therefore preferably setmore or less horizontally (so that the flail blade 6 pivotssubstantially in the horizontal plane as per convention) approximately10 millimeters above the cutting height G. The rotationally forward edgeof the flail blade 6 is twisted downwards at an increasing angle towardsthe outer end of the flail blade 6, to the desired cutting height G asdepicted by T in FIGS. 9a and 9b, while the outer end of the trailingedge is twisted upwards to form a small fin 7.

The incorporation of a small step in the flail blade 6 as shown in FIG.9b has been found beneficial, to lower the inclined trailing edge fin 7of the flail blade 6 sufficiently to permit the flail blade 6 to retractpivotally in a full circle, obviating the possibility of the flail blade6 striking the vane 3 from which the flail blade 6 depends. Thisminimizes possible damage to the flail blade 6 as well as to thesupporting vane 3, and also avoids jamming of the flail blade 6 againstor beneath the vane 3 when an obstruction to the flail blade 6 isencountered.

This blade design significantly reduces the likelihood of deforming thecrankshaft or damaging the blade housing or blade assembly itself, whilefacilitating the replacement of the primary wear elements easily andcost effectively.

A high solidity ratio impeller has the advantage of allowing stiff butlight fabrication, providing stable mounting points for the primarycutting blades or flail blades 6.

The occlusion provided by fie central body 1 of the preferred embodimentshields the shaft 24, and thereby discourages flax and other long leafvegetation as well as rope and the like from becoming entangled aroundthe mower or engine shaft 24. As mulching blades by design inducecirculation F inwards toward the said blade shaft 24, they areparticularly prone to entangling such impediments around the blade ordrive shaft Therefore a mulching blade with the means for helping toavoid or at least reduce this problem is of particular advantage.

The preferred embodiment of the present invention is also found toreduce noise and turbulence set up inside the blade housing, due to therelatively even distribution of air-impelling faces, both across andaround the assembly, resulting in a generally smoother and quieteroperation than many conventional blade assemblies.

The present invention has the tendency to begin to recut andconsequently disperse excess clippings back into the lawn if outflowfrom the discharge chute 25 is prevented, such as once the catcher isfull. This helps to avoid clogging of the blade housing 21 with untaughtclippings which may otherwise cause the engine to eventually stall, aswell as forestailing the need to empty the catcher, thus allowing theuser to empty the catcher at his or her convenience.

Safety is also enhanced with this system, as there is likewise lessenedtendency for clippings to build up and become clogged in the dischargechute 25 once the cateher is full, which may otherwise tempt the user totry to clear the clogged discharge chute 25 while the blades are inmotion.

Further to these points, a high solidity ratio impeller also presentssmaller openings 4 for the intrusion of solid objects, sticks, rods andthe Like between the impeller vanes 3, which objects could cause damageto either the impeller itself or to the engine or blade shaft 24 onwhich it depends. It is to be appreciated that the higher the solidityratio becomes, the less the chance of insertion of an object between thevanes 3.

Pivotally mounted flail blades 6 have been found to have severaladvantages over non-pivoting blade tips, such as reducing the risk ofdamaging the blade housing 21, the impeller assembly, the engine orblade shaft 24 or engine itself 22 of a rock, tree root or otherimpediment is struck by the said flail blade 6, as the pivoting actionof the flail blade 6 reduces the likelihood of abruptly halting therotation of the blade and shaft 24 assembly, thereby lessening thelikelihood of deforming the engine 22 or blade shaft 24. While usingflexible wire as the primary cutting element as described in U.S. Pat.No. 49,245, in conjunction with separate fins or other means forproducing uplift at the outer periphery of the blade is anotheralternative, pivoting flail blades 6 are preferred for simplicity.

The weight of the preferred assembly is generally less than that of acomparable size disc and flail blade assembly. This has a number ofadvantages, namely reducing the weight of the assembly for fabrication,handling and transport; lowering the cost of the material itself forboth purchasing and treating; lowering the inertia of the assembly foraiding both starting the engine and stopping rotation within a minimumtime from switching the motor off.

It will be appreciated that the provision of these secondary featuresand/or advantages in the preferred embodiment does not comprise theobject of the invention, and that alternative embodiments which fall toprovide any one or more such advantages may nonetheless fall within thescope of the present invention.

In summation, providing a strong rotational and circumferential airflowand regulating the downward airflow, in addition to generating tipvortices and swirl, is advantageous for coping with wet, lush grass,cross-sectional housing variations and restrictions, and other variablefactors influencing mulching and/or catching performance. The airflowalso has advantages when catching discharged clippings, such as improvedparticle size and speed at which particles are discharged, as well asless clogging of clippings inside the blade housing.

It will be appreciated that alterations to the preferred embodimentdescribed above may improve performance in one area at the expense ofperformance in another area.

ALTERNATIVE EMBODIMENTS

An alternative embodiment is shown in perspective view in FIG. 11, whichincorporates scoops formed out of a complete disc. This embodiment is atpresent considered less preferable than that shown in FIGS. 1 to 9--itdoes not produce tip vortices at the edge of the inner region,manufacture is more difficult, and the overall weight of the assembly isgreater.

Another embodiment as shown in perspective in FIG. 12 is the provisionof a solid disc, of less diameter than the preferred disc describedabove. At least four flail blades with means for producing uplift,downdraft and strong circumferential circulation are provided, ofsufficiently increased length to compensate for the smaller diameterdisc. Raising the front edge of the flail blades inwardly from theprimary cutting and uplift area to encourage downdraft, as well assharpening the leading edge of said flails in this inner position alsois beneficial. The use of a blade housing of substantially flat, uniformcross section above the said flail blades, preferably within 100 mm orso but with ample clearance, has also been found beneficial, as saidroof tends to deflect the uplifted air and clippings and direct themdown into the lawn.

This embodiment is more reliant on the shape of the blade housing,although increased circumferential circulation is generated and aids thedispersal of clippings back into the lawn. Some of the advantagesrealized with the preferred embodiment are lost, such as the ability tooperate independently of the blade housing shape. Furthermore, theweight of such a solid disc is not desirable. Hence this embodiment,while possibly allowing easier and more cost effective fabrication, isnot viewed as preferable.

Other changes and modifications might also be made within the generalspirit and scope of the invention, which may be characterized by thefollowing claims.

I claim:
 1. A blade assembly for a rotary cutter, comprising:means (2)for mounting the blade assembly on a central shaft (24); a generallyplanar body substantially evenly disposed about said mounting means (2),said body having an inner region and a peripheral region; means (15) forcutting in the peripheral region; means (7) for creating an updraft inthe peripheral region; means (3) for creating a downdraft in the innerregion; and means (3, 7) for creating a rotational airflow in theperipheral region, said means (3, 7) having a radially and an axiallyextending face area of said body, by which air can be moved as said bodyrotates on said central shaft (24); characterized in that said face areaof said inner region is greater than said face area of said peripheralregion; further characterized in that said means (7) for creatingupdraft includes a plurality of outwardly projecting generally planarblades in said peripheral region, each of said blades being at least inpart inclined upwards between a leading edge (9) and a trailing edge (8)relative to a direction of rotation of the blade assembly; andfurthermore characterized in that said blades are twisted substantiallydownwards at outer ends, to a level below a lower edge of the body.
 2. Ablade assembly according to claim 1, characterized in that four bladesare provided.
 3. A blade assembly according to claim 1, characterized inthat said leading edge includes said cutting means (15).
 4. A bladeassembly according to claim 1, further characterized in that said bladesare fixed substantially parallel to a general plane of said body, andtwisted both downwards at the rotationally leading edge (9) and upwardsat the rotationally trailing edge (8) towards the outer ends, to createsaid uplift.
 5. A blade assembly for a rotary cutter, comprising:means(2) for mounting the blade assembly on a central shaft (24); a generallyplanar body substantially evenly disposed about said mounting means (2),said body having an inner region and a peripheral region; means (15) forcutting in the peripheral region; means (7) for creating an updraft inthe peripheral region; means (3) for creating a downdraft in the innerregion; and means (3, 7) for creating a rotational airflow in theperipheral region, said means (3, 7) having a radially and an axiallyextending face area of said body, by which air can be moved as said bodyrotates on said central shaft (24); characterized in that said face areaof said inner region is greater than said face area of said peripheralregion; further characterized in that said inner region has a plansolidity ratio to swept area of greater than 0.5.
 6. A blade assemblyaccording to claim 5, characterized in that said means (3) for creatingthe downdraft and said means (3, 7) for creating the rotational airflowinclude vanes (3) in said body angled downwards from a leading edge (9)to a trailing edge (8) relative to a direction of rotation.
 7. A bladeassembly according to claim 6, characterized in that four vanes (3) areprovided.
 8. A blade assembly according to claim 6, characterized inthat said vanes (3) are of similar chord at a tip (W) as at a root (W').
 9. A blade assembly according to claim 5, further comprising means forcreating a toroidal vortex between said inner region and said peripheralregion of the body.
 10. A blade assembly according to claim 9,characterized in that said means (3) includes vanes (3) being chamberedupwards towards the central shaft (4) to form a radially extending ridge(11), to create a pressure differential between upper and lower surfacesof said vanes (3) in use, thus inducing the toroidal vortex.
 11. A bladeassembly according to claim 19, wherein said vanes (3) extend radiallyoutwards over at least half a radius of said inner region of the body.12. A blade assembly according to claim 5, characterized in that saidplan solidity ratio is between 0.6 and 0.8.
 13. A blade assembly for arotary cutter, comprising:means for mounting the blade assembly on acentral shaft; a generally planar body substantially evenly disposedabout said means for mounting on the central shaft, said body having aninner region and a peripheral region; means for cutting in theperipheral region; means for creating an updraft in the peripheralregion; means for creating a downdraft in the inner region; and meansfor creating a toroidal vortex between said inner region and saidperipheral region; a plan area of said inner region is greater than aplan area of said peripheral region; wherein said means for creating atoroidal vortex includes a plurality of vanes being cambered upwardstowards a center of each vane to form a radially extending ridge, tocreate a pressure differential between upper and lower surfaces of saidvanes in use, thus inducing the toroidal vortex.
 14. A blade assemblyfor a rotary cutter, comprising:means for mounting the blade assembly ona central shaft; a generally planar body substantially evenly disposedabout said means for mounting on the central shaft, said body having aninner region and a peripheral region; means for cutting in theperipheral region; means for creating an updraft in the peripheralregion; means for creating a downdraft in the inner region; and meansfor creating a rotational airflow, having a radially and an axiallyextending face area of said body, by which air can be moved as said bodyrotates on said central shaft; wherein a plan area of said inner regionis greater than a plan area of said peripheral region and said innerregion has a plan solidity ratio to swept area of greater than 0.5. 15.A blade assembly according to claim 14, characterized in that said plansolidity ratio is between 0.6 and 0.8.
 16. A blade assembly for a rotarycutter, comprising:means for mounting the blade assembly on a centralshaft; a generally planar body substantially evenly disposed about saidmeans for mounting on the central shaft, said body having an innerregion and a peripheral region; means for cutting in the peripheralregion; means for creating an updraft in the peripheral region; meansfor creating a downdraft in the inner region; and means for creating arotational airflow, having a radially and an axially extending face areaof said body, by which air can be moved as said body rotates on saidcentral shaft; wherein a plan area of said inner region is greater thana plan area of said peripheral region and a plurality of blades istwisted substantially downwards at outer ends of the blades, to a levelbelow a lower edge of the body.
 17. A blade arrangement for a rotarycutter, comprising:a body mountable for rotation about a substantiallyvertical, rotational, central axis; said body having a peripheral regionwhich is provided with cutting means which project outwardly and meansfor creating an updraft in a space swept out by the body as the bodyrotates about the central axis; said body also having an inner regionwhich is located between the peripheral region and the central axis;said inner region being provided with means for creating a downdraft ina space located between the peripheral region and the central axis; saidinner region also having a plurality of projections which are spacedabout the central axis and which extend outwardly therefrom; at leasttwo of said projections each carrying one of the cutting means whichproject outwardly; and said projections each having a leading edge whichis angularly spaced from a leading edge of each cutting means and whichangularly intersects an outer edge of each projection.
 18. A bladearrangement according to claim 17, in which the inner region has asolidity ratio of not less than 0.5.
 19. A blade arrangement accordingto claim 18, in which the solidity ratio is between 0.6 and 0.8.
 20. Ablade arrangement according to claim 17, in which each of said at leasttwo projections includes a vane that is angled downwardly from a leadingedge to a trailing edge of the vane for creating the downdraft when thebody is rotated.
 21. A blade arrangement according to claim 20, in whichthe vane carries the cutting means that projects outwardly.
 22. A bladearrangement according to claim 21, in which the vane has a camberedformation for creating the downdraft, said cambered formation extendingfrom the leading edge of the vane towards the trailing edge of the vane.23. A blade arrangement according to claim 21, in which the cuttingmeans is twisted substantially downwards at the outer end thereof sothat the leading edge thereof is located below the vane.
 24. A bladearrangement according to claim 20, in which the leading edge of the vaneangularly intersects the outer edge of each projection and also whereinthe leading edge of each cutting means is angularly spaced from theleading edge of the vane.
 25. A blade arrangement according to claim 24,in which the cutting means is shaped to create the updraft.
 26. A bladearrangement according to claim 25, in which the cutting means has awidth which is less than a width of the vane.
 27. A blade arrangementaccording to claim 26, in which the cutting means is located adjacent tothe trailing edge of the vane.
 28. A blade arrangement according toclaim 24, in which the inner region and the peripheral region each havea radially and an axially extending face area, said face area of theinner region being greater than the face area of the peripheral region.29. A blade arrangement according to claim 28, in which the body hasfour vanes and four cutting means mounted one on each vane.
 30. A bladearrangement according to claim 24, in which the vane has a root having awidth that is similar to the width of the vane at the outer edgethereof.
 31. A blade arrangement according to claim 30, in which thevane extends outwardly over at least half of the inner region.
 32. Ablade arrangement according to claim 24, further comprising:means forcreating a toroidal vortex between the inner region and the peripheralregion.
 33. A blade arrangement according to claim 20, in which the vaneincludes a cambered region extending outwardly from the central axis andbeing disposed between the leading edge of the vane and the trailingedge of the vane.
 34. A blade arrangement according to claim 33, inwhich the vane has a flat region disposed between the cambered regionand the trailing edge, said cutting means being pivotably mounted on theflat region.